A variety of different signal detectors have been developed in the past, and, indeed, many electronic circuits include tuning circuitry adapted to receive, filter and process signals within a selected frequency range. With respect to signal detectors constructed specifically to monitor a broad range of oscillatory signals, certain problems arise where those circuits seek signals having certain selected frequency characteristics. For example, many of the existing detectors exhibit a high susceptibility to noise and produce faulty readings where random noise signals fall within the target frequency range. Further, these systems often encounter problems with signal to noise ratio for the target signals versus the background noise. In order to solve these problems, many existing signal detectors resort to superheterodyning in order to increase sensitivity, eliminate noise and shift frequency bands.
The present invention generally concerns the detection of selected target oscillatory signals within a defined universe of that type of oscillatory signal. Thus, this invention may be used for signals in the electromagnetic spectrum, acoustic signals, etc. An example discussed in detail to explain the principles of this invention concerns the detection of ultrasonic signals in an ambient sound environment. The desirability of these devices has been recently increasing due to the recognition that ultrasonic detectors may readily be implemented as leak detectors to detect ultrasonic signals which, for example, are created by the escape of pressurized gasses through small openings. This is useful, for example, in detecting leakage from pipelines as well as in detecting air flow paths, for example, through insulation of houses and commercial buildings and through automobile doors and panels. Other analytical values of such ultrasonic detectors are being discovered as well.
In the background portion of my U.S. Pat. No. 5,103,675, I described existing technology of ultrasonic signal detection and processing in order to explain advantages of the specific ultrasonic signal detection system and method set forth and claimed therein. However, the principles and circuitry for signal detection and processing have broader application to signals other than ultrasonic acoustical signals. Therefore, the present division of the patent application that resulted in U.S. Pat. No. 5,103,675 concerns the detection and/or processing oscillatory signals, in general, whether such signal is found within a circuit (e.g. an electrical or optical circuit), in an electromagnetic transmission (e.g. television, microwave, radio, etc.), in an acoustic environment, or in other environments that may be known in the art. In these environments, there remains a need for a signal detectors and processing methodologies that are both sensitive in operation and which can operate to detect the large range of target frequencies. Further, there is a need for a signal detectors and that are less susceptible to mechanical vibration and temperature change. There is a further need for signal detectors and processing methodologies that are more effective at filtering noise signals in order to get a cleaner target signal detection.